As image technology develops rapidly, mobile smart terminals have gradually replaced cameras and become an important tool used in our daily life for taking pictures and making a video. Meanwhile, as users of mobile terminals become more and more professional, their requirements on the quality of the images taken with mobile terminals are getting higher and higher, wherein the dynamic range of an image has become an important factor valued by a user when judging the quality of the image.
The dynamic range of an image refers to a range starting from the ‘darkest’ part of the image and ending with the ‘brightest’ part of the image. The larger the dynamic range of an image is, the more gradations the image presents, and the more dark details and bright details the image records. The dynamic range is determined by a photosensitive element, and the dynamic range of a photosensitive element is set unchangeably after the photosensitive element is delivered. In the field of mobile smart terminals, due to the various limitations to the volume and the structure of smart terminals, smart terminals get smaller and smaller in size and higher and higher in pixel value, as a result, the effective light-sensing area of a single pixel becomes smaller and smaller, which affects the dynamic range of a camera. Therefore, it occurs often that in an image obtained by taking a scene where light changes remarkably in brightness, the dark part is too dark or a bright part is too bright, leading to the loss of details in the image and a reduction in the quality of the image.